Optical Monitoring of Three Gamma-Ray-loud BL Lacertae Objects in 1999-2002

Zhang, Xiang; Zhang, L.; Zhao, Gong-Bo; Xie, Zhao-Hua; Lin, Wei; Zheng, Y. G.

doi:10.1086/424537

Cited by 31 publications

(20 citation statements)

References 56 publications

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“…A bluer-when-brighter behaviour was also detected by other authors in datasets more or less extended in time (e.g. Zhang et al 2004;Stalin et al 2006;Gu et al 2006).…”

Section: Introductionsupporting

confidence: 78%

The nature of optical and near-infrared variability of BL Lacertae

Larionov

Villata

Raiteri

2010

A&A

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Context. Since 1997, BL Lacertae has undergone a phase of high optical activity, with the occurrence of several prominent outbursts. Starting in 1999, the Whole Earth Blazar Telescope (WEBT) consortium has organised various multifrequency campaigns on this blazar, collecting tens of thousands of data points. One of the main issues in the analysis of this huge dataset has been the study of colour variability. Aims. The immense amount of optical and near-infrared data collected during the campaigns enables us to perform a thorough analysis of multiband data, with the aim to understand the flux variability mechanisms. Methods. We use a new approach for the analysis of these data, focusing on the source spectral evolution. Results. We show that the overall behaviour of the BL Lacertae light and colour curves can be explained in terms of a changing viewing angle of a moving, discrete emitting region, which causes variable Doppler boosting of the corresponding radiation. Conclusions. A fractal helical structure is suggested to be at the origin of the different time scales of variability.

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“…A bluer-when-brighter behaviour was also detected by other authors in datasets more or less extended in time (e.g. Zhang et al 2004;Stalin et al 2006;Gu et al 2006).…”

Section: Introductionsupporting

confidence: 78%

The nature of optical and near-infrared variability of BL Lacertae

Larionov

Villata

Raiteri

2010

A&A

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“…The largest optical variations registered are on the order of 3-4 mag (Pollock et al 1979;Fan et al 1997) at long (years) ranges. Some intra-day (IDV) and inter-day variations until 0.5 mag were reported in the optical history of this blazar (Xie et al 1992;Fan et al 1997;Massaro et al 1995;Zhang et al 2004). Over the period 1995-1997, the optical IDV and microvariations were rare and with a small amplitude (Bai et al 1999), while no clear evidence was found in more recent observations (Sagar et al 2004).…”

Section: Optical Properties Of Pks 0735+178mentioning

confidence: 94%

Ten-year optical monitoring of PKS 0735+178: historical comparison, multiband behavior, and variability timescales

Ciprini

Takalo

Tosti

et al. 2007

A&A

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Aims. New data and results on the optical behaviour of the prominent blazar PKS 0735+178 (also know as OI 158, S3 0735+17, DA 237, 1ES 0735+178, 3EG J0737+1721) are presented, through the most continuous BV RI data available in the period 1994-2004 (about 500 nights of observations). In addition, the whole historical light curve, and a new photometric calibration of comparison stars in the field of this source are reported. Methods. Several methods for timeseries analysis of sparse data sets are developed, adapted and applied to the reconstructed historical light curve and to each observing season of our unpublished optical database on PKS 0735+178. Optical spectral indexes are calculated from the multi-band observations and studied on long-term (years) durations as well. For the first time in this source, variability modes, characteristic timescales and the signal power spectrum are explored and identified over 3 decades in time with a sufficient statistics. The novel investigation of mid-term optical scales (days, weeks), could be also applied and compared to blazar gamma-ray light curves that will be provided, on the same timescales, by the forthcoming GLAST observatory. Results. In the last 10 years the optical emission of PKS 0735+178 exhibited a rather achromatic behaviour and a variability mode resembling the shot-noise. The source was in a intermediate or low brightness level, showing a mild flaring activity and a superimposition/succession of rapid and slower flares, without extraordinary and isolated outbursts but, at any rate, characterized by one major active phase in 2001. Several mid-term scales of variability were found, the more common falling into duration intervals of about 27-28 days, 50-56 days and 76-79 days. Rapid variability in the historical light curve appears to be modulated by a general, slower and rather oscillating temporal trend, where typical amplitudes of about 4.5, 8.5 and 11-13 years can be identified. This spectral and temporal analysis, accompanying our data publication, suggests the occurrence of distinctive signatures at mid-term durations that can likely be of transitory nature. On the other hand the possible pseudo-cyclical or multi-component modulations at long times could be more stable, recurrent and correlated to the bimodal radio flux behaviour and the twisted radio structure observed by several years in this blazar.

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“…Optical IDV up to 0.5 mag has been reported in the source on some occasions (e.g. Xie et al 1992;Massaro et al 1995;Fan et al 1997b;Zhang et al 2004). PKS 0735+178 has shown a high degree of optical and near-infrared polarizations which varies from 1% to 30% (e.g.…”

Section: Idv and Short-term Variability Of Individual Blazarsmentioning

confidence: 95%

Optical Intra-Day Variability in Blazars

Gupta

Jiang

Bai

et al. 2008

The Astronomical Journal

121

152

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We selected a sample of a dozen blazars which are the prime candidates for simultaneous multi-wavelength observing campaigns in their outburst phase. We searched for optical outbursts, intra-day variability (IDV) and short-term variability in these blazars. We carried out optical photometric monitoring of nine of these blazars in 13 observing nights during our observing run of 2006 October 27-2007 March 20 using the 1.02 m optical telescope equipped with CCD detector and BVRI Johnson broadband filters at Yunnan Astronomical Observatory, Kunming, China. From our observations, our data favor the hypothesis that three blazars, AO 0235+164, S5 0716+714, and 3C 279, were in the outburst state; one blazar, 3C 454.3, was in the post-outburst state; three blazars, S2 0109+224, PKS 0735+178, and OJ 287, were in the pre/post-outburst state; one blazar, ON 231, was in the low state; and the state of one blazar, 1ES 2344+514, was not known because there are not many optical data available for the blazar to compare with our observations. We observed densely sampled 1534 image frames of these nine blazars. Out of three nights of observations of AO 0235+164, IDV was detected in two nights. Out of five nights of observations of S5 0716+714, IDV was detected in two nights. In one night of observations of PKS 0735+178, IDV was detected. Out of six nights of observations of 3C 454.3, IDV was detected in three nights. No IDV was detected in S2 0109+224, OJ 287, ON 231, 3C 279, and 1ES 2344+514 in their one, four, one, two, and one nights of observations, respectively. AO 0235+164, S5 0716+714, OJ 287, 3C 279, and 3C 454.3 were observed in more than one night and short-term variations in all these blazars were also noticed. From our observations and the available data, we found that the predicted optical outbursts with time intervals of ∼8 years in AO 0235+164 and ∼3 years in S5 0716+714 have possibly occurred.

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Optical Monitoring of Three Gamma-Ray-loud BL Lacertae Objects in 1999-2002

Cited by 31 publications

References 56 publications

The nature of optical and near-infrared variability of BL Lacertae

The nature of optical and near-infrared variability of BL Lacertae

Ten-year optical monitoring of PKS 0735+178: historical comparison, multiband behavior, and variability timescales

Optical Intra-Day Variability in Blazars

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